Running the setup.exe file for ArcView 3.x on a Windows machine returns the error:
"Win16 subsystem was unable to enter protected mode, dosx.exe must be present in your path."
The DOS environment is not properly configured to run 16-bit applications such as ArcView's setup file.
This line may exist but be proceeded by a "REM", which prevents it from being read. Remove the "REM" if this is the case.
If there are other "devices" specified, add "REM" to the line to prevent it from being used in the DOS settings during the ArcView install. It is possible to remove the "REM" once setup is complete.